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From July 12, 2000, through September 18, 2001, a total of 21 cases
of poliomyelitis (including two fatal cases) were reported from the Caribbean island
of Hispaniola, divided between Haiti and the Dominican Republic
(1,2). In the Dominican Republic, 13 of 168 reported cases of acute flaccid paralysis (AFP) were confirmed
as polio by isolation of poliovirus type 1 from either patients or their healthy contacts.
The median age of the patients was 3 years (range: 9 months--14 years). None
was vaccinated adequately. The most recent confirmed case-patient in the
Dominican Republic had paralysis onset on January 25, 2001. In Haiti, eight of 40 AFP cases
were confirmed virologically; seven of the confirmed cases occurred during
January--July 2001. The median age of the patients was 7 years (range: 2--12 years). One
patient had received at least 3 doses of oral poliovirus vaccine (OPV). The most
recent confirmed case occurred in Haiti and the patient had paralysis onset on July 12,
2001. Eighteen AFP cases from the Dominican Republic and three from Haiti are
pending final classification.

This outbreak was the first in the Americas since 1991 and was associated with
the
circulation of a type 1 OPV-derived virus, having substitutions affecting 1.8% to 4.1%
of nucleotides encoding the major capsid protein (VP1). The circulating
vaccine-derived poliovirus associated with the outbreak recovered the capacity to cause
paralytic disease and widespread person-to-person transmission and was
biologically indistinguishable from type 1 wild poliovirus. Contemporary vaccine-derived
poliovirus isolates from persons with AFP cases in other countries of the Americas are
more closely related (>99.5% VP1 sequence similarity) to the respective OPV strains,
are unrelated to the Hispaniola outbreak viruses, and show no evidence of
extensive person-to-person transmission. The outbreak in Hispaniola occurred in areas of
very low OPV coverage.

In response to the outbreak, health authorities in both countries conducted
house-to-house vaccination with OPV. Three rounds of mass vaccination campaigns
were conducted in the Dominican Republic in December 2000, and February and April
2001. In each round, approximately 1.2 million OPV doses were administered to
an estimated population of 1.1 million children aged <5 years. Haiti conducted two
rounds of mass vaccination in February and March 2001. However, these campaigns
were hampered by logistic difficulties and heavy rains and reached an estimated 40% of
the 1.2 million children aged <5 years. During May--July 2001, a door-to-door and
school-based campaign among all 2.3 million children aged <10 years was
conducted sequentially in all of the country's departments. Preliminary results suggest that
2.4 million OPV doses were administered, and a second door-to-door campaign is
under way.

Travelers to the Dominican Republic and Haiti who are not vaccinated
adequately are at risk for polio. Travelers should have received poliovirus vaccination according
to national vaccination policies (3).

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